The present invention relates to fluid treatment apparatus and particularly, although not exclusively, to apparatus for the treatment of slurries comprising solids in liquids. One problem encountered with the treatment of process fluids lies in the potential contamination of such fluids with other material, particularly particles of metal, glass, stones and the like. Obviously such materials are not affected by the bacteriological treatment to which the process fluid is subject, and, moreover, can lead to a build up of unwanted solids in the treatment plant.
The present invention thus seeks to provide means by which such inorganic solids, or indeed, organic solids where these are sufficiently dense or aggregated in sufficiently large particles such as not to be broken down by any bacteriological process taking place in the chamber during the residence time of the material within the treatment apparatus, may be removed from the treatment apparatus for further processing prior to separate treatment recycling or reintroduction to the treatment apparatus.
One technical field in which such slurries occur is in the treatment of organic material by bacteriological action, especially the so-called slurry digestion processes which are known for the treatment of organic waste materials. In the treatment of process fluids both with bacteriological and other processes problems can arise from the possibility of non-uniform treatment due to differences in the conditions encountered by the process fluid as it passes through the treatment system, and especially on differences in the residence time of the material within the system.
Where bacteriological action is involved, which frequently takes a relatively extended time period for completion, any material which follows a shorter than average route through the process material may be inadequately treated. This is unacceptable in the circumstances where the treatment processes is a biological breakdown of waste products because the resulting, partially-treated material may not be suitable for the uses to which the fully-treated material may be put.
For example, biological breakdown of organic waste material such as animal excrement produces, when the treatment is complete, a residual solid material which is odour free and high in nutrients suitable for use as a horticultural or agricultural fertiliser. Inadequately treated material, on the other hand, may not be odour free, and more importantly may contain biological contaminants, pathogens or seeds the former of which could be dangerous or at least detrimental and the latter of which, if still viable way reduce the value of the material as a fertiliser.
Known apparatus for treatment of process fluid includes that described in the applicant""s own earlier GB Patent Application No. 9519499.9 and PCT/GB96/02336 (Publication No. 97/11915) which describes an elongate tank of so-called xe2x80x9ccardioidxe2x80x9d cross section within which the process fluid is caused to circulate by the introduction of gas bubbles at a low level which, as they rise through the process fluid, urge it to circulate and thus maintain entrained solids in suppression. The use of gas bubbles to divide circulation is also known from U.S. Pat. No. 5,041,216, which describes a fluidised bed reaction having an outlet at a high level with a filter cage to act as a retention system arranged on the
According to the present invention there is provided treatment apparatus comprising a treatment chamber for receiving a process fluid, in which there are provided means for introducing gas at a level within the chamber such as to create bubbles which rise through the fluid characterised in that there are provided means in the vacinity of the gas inlet openings for collecting solid particles entrained with the process fluid which sink as a consequence of contact with the bubbles.
This allows a preliminary separation of relatively heavy solid particles to take place.
In one embodiment of the present invention apparatus for treatment of process fluids is so arranged that the residence time of the fluid within the apparatus is at least more nearly uniform for all of the process material regardless of its density or composition.
This minimises the risk of non-uniform treatment by ensuring that all component parts of a process fluid must follow the spiral path first radially in one direction (for example radially outwardly)and then in the other direction (for example radially inwardly). This effect may further be enhanced by ensuring that the inlet and outlet of process fluid to and from the treatment vessel are at opposite ends thereof.
Another embodiment of the invention comprises treatment apparatus in which a chamber for receiving a treatment fluid has at least two generally unobstructed interior regions in each of which the process fluid is caused to follow a circulating path, in which the means defining overall paths of different parts of the process fluid between an inlet and an outlet to the chamber result in the path lengths being not substantially different for all parts of the process fluid.
Embodiments of the present invention may be formed as a treatment vessel for a process involving biological action on organic process materials comprising a solid/liquid or liquid/liquid slurry or mixture, in which circulation of the process material is driven by introducing gas at a low level within the vessel and allowing bubbles thereof to rise, with a collection region for solids from which solids can be extracted for further treatment.
In a preferred embodiment of the invention the bubble inlets are arranged in a plurality of rows thereof whereby to provide a xe2x80x9ccurtainxe2x80x9d of bubbles. In a vessel configuration such as that outlined above, in which the vessel has two regions in which the process fluid is caused to circulate in opposite directions, and in which the transfer of the process fluid from one to the other takes place in its transit through the vessel, the circulation-driving bubbles may form a xe2x80x9ccurtainxe2x80x9d between the two regions such that the process fluid must pass across the curtain of bubbles in its transit through the vessel. Any relatively dense particle of solid material entrained with the process fluid will, on passing through the bubble curtain, experience a significant reduction in its buoyancy thereby falling to the solids-collection region.
A configuration in which two rows of bubble inlets are provided may have a channel between the two rows of bubble inlets serving as this collection region, and such channel may house an auger or other means for driving the solid particles collecting therein towards a distribution point from which they can be removed from the vessel.
Removal of such solids from the vessel may involve the use of a water column within which the solids may be elevated, for example by means of a further auger or a gas lift apparatus, add which serves to maintain the gas tight closure of the vessel while nevertheless allowing solids to be extracted therefrom.
There may be provided a screen above the said solid particle collection means, in the vacinity of the bubbles created by the gas introduction means, whereby to assist in the separation of particles such screen may be orientated to be in a substantially vertical or slightly inclined plane.
As an example, one embodiment of the present invention may comprise a treatment system for a process fluid comprising or including organic materials to be broken down by bacteriological action, comprising a plurality of chambers interconnected to receive the process fluid in sequence, each chamber having means for controlling at least one process parameter, and means for introducing fluid into the chamber in addition to the process fluid. There may further be provided means for directing process fluid from the outlet of a chamber to an inlet of the same chamber or to an inlet of another chamber upstream or downstream in relation to the flow of process fluid through the system.
The parameters which may be controlled within the chambers comprise the temperature of the process fluid within the chamber, the pressure within the chamber, the rate of flow of process fluid through the chamber, the precise bacteriological content of the chamber (in the case of biological processes, which may be achieved by introducing particular bacteria into it for inoculating the material therein) and/or the introduction or presence of other process reagents, in particular liquids or gases.
The introduction of a gas into the treatment vessel may be undertaken simply to drive the circulation of the process fluid within the vessel, in which case the gas may be chosen as one contributing to the maintenance of aerobic or anaerobic conditions as the case may require, or alternatively the gas may be one which takes part in the reaction proceeding within the vessel.
Whether the plurality of chambers are formed as compartments within a vessel by partitioning, or whether they are formed as separate vessels interconnected by ducting, it is preferred that at least some of the walls defining the chamber are in contact with a heat exchange fluid which can be driven in counter current with respect to the direction of flow of process fluid through the system. In this way, for example, exothermic reactions taking place in some of the chambers can be cooled by the heat exchange fluid and the heat transferred to other chambers whereby to raise the temperature of the material therein.